Spectrophotometric determination of iodide at the 10–6 mol l–1 level by solvent extraction with methylene blue

Abstract

Iodide is separated from other chemical species by its oxidation and subsequent extraction into carbon tetrachloride. The proposed method is based on the extraction of the back-extracted iodide into 1,2-dichloroethane as an ion pair with methylene blue. When a 40-ml sample solution is used, the apparent molar absorptivity for iodide is 3.15 × 10⁵ l mol^–1 cm^–1 and the Sandell sensitivity for a 0.001 absorbance is 4.3 × 10^–4µg cm^–2 of l^– at 657 nm. A linear calibration graph is obtained over the range 7.5 × 10^–8–3 × 10^–6M iodide and the relative standard deviation is 0.87% at the 1.5 × 10^–6M iodide level. The proposed method was successfully applied to the determination of various amounts of iodide in natural water samples.